1. Field of the Invention
The present invention relates to a droplet jetting apparatus having a droplet jetting head in which a specific liquid is jetted as droplets from nozzle openings and a capping device for capping a nozzle opening of the droplet jetting head so as to prevent drying of the liquid or clogging of the nozzle opening, and also relates to a method of operating the droplet jetting apparatus and to a device manufacturing method.
Priority is claimed on Japanese Patent Application No. 2004-023872, filed Jan. 30, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
Generally, a droplet jetting head includes a pressure generating chamber for containing a specific liquid, a piezo actuator for compressing the pressure generating chamber, and a nozzle opening communicated with the pressure generating chamber. The liquid in the pressure generating chamber is compressed by the piezo actuator, thereby jetting a small amount of liquid from the nozzle opening as a droplet. In the droplet jetting head having the above structure, if liquid in the neighborhood of the nozzle opening is evaporated or if air bubbles remain inside the droplet-jetting head, a problem occurs in droplet jetting. Therefore, the above kind of droplet jetting head requires a capping device for capping or sealing the nozzle opening so as to prevent drying of the liquid or clogging of the nozzle opening.
The capping device includes a capping portion for capping the nozzle opening and an attraction pump for supplying negative pressure to the inside of the capping portion. The capping device not only caps the nozzle opening of the droplet jetting head by using the capping portion but also applies negative pressure to the capping portion by using the attraction pump so as to forcedly discharge the liquid from the nozzle opening, thereby discharging the liquid having increased viscosity in the neighborhood of the nozzle opening or air bubbles remaining in the pressure generating chamber.
Detailed descriptions about the conventional droplet jetting apparatus having the above-explained droplet jetting head and the capping device are found, for example, in Japanese Unexamined Patent Application, First Publication No. 2001-018408.
In the droplet jetting apparatus disclosed in the above document, an absorbent material is provided in the capping portion. When no printing is performed or the power source is off, a specific quantity of moisture retentive liquid is supplied in advance from a moisture retentive liquid tank to the absorbent material before capping of the nozzle opening, so as to reduce evaporation of the liquid from the nozzle opening after the capping, thereby maintaining the moist atmosphere in the capping portion.
However, droplets of the moisture retentive liquid drop from the moisture retentive liquid tank which is mounted on a carriage; thus, the size and the weight of the carriage is increased and increase in the cost for a carriage motor is unavoidable.
In addition, even when the nozzle opening of the droplet jetting head is capped using the capping device, if the capped state continues for a long period of time, increase in the viscosity of the liquid may occur due to decrease in moisture retention which is caused by evaporation of the liquid in a passage for the liquid or from a nozzle opening, or by drying in the capping device, so that the nozzle opening may be clogged. Accordingly, there is a demand to supply moisture retentive liquid to the capping portion at regular intervals after capping the nozzle opening, while maintaining the capped state of the nozzle opening.
As another method for clearing the clogging of the nozzle opening, other than the method of using a capping device, (i) a cleaning method is known, in which negative pressure is applied to a nozzle formation surface (i.e., a surface in which nozzle openings are formed) of the droplet jetting head so as to attract the liquid from the nozzle openings, and the nozzle forming plane is cleaned using a wiper after the attraction of the liquid, or (ii) a flushing method is known, in which the pressure applied to the pressure generating chamber by using the piezoelectric element is increased so as to forcedly jet droplets greater than a normal quantity of jetted droplets. However, in the above methods, the liquid is uselessly consumed and the life of the droplet jetting head or the wiper is reduced.